Method and system for directional enhancement of sound using small microphone arrays
View Patent ↗Herein provided is a method and system for directional enhancement of a microphone array comprising at least two microphones by analysis of the phase angle of the coherence between at least two microphones. The method can further include communicating directional data with the microphone signal to a secondary device, and adjusting at least one parameter of the device in view of the directional data. Other embodiments are disclosed.
1. A method, practiced by way of a processor, to increase a directional sensitivity of a microphone signal comprising the steps of:
capturing a first and a second microphone signal communicatively coupled to a first microphone and a second microphone;
calculating a complex coherence between the first and second microphone signal;
determining a measured frequency dependent phase angle of the complex coherence;
comparing the measured frequency dependent phase angle with a reference phase angle threshold and determining if the measured frequency dependent phase angle exceeds a predetermined threshold from the reference phase angle;
updating a set of frequency dependent filter coefficients based on the comparing to produce an updated filter coefficient set; and
filtering the first microphone signal or the second microphone signal with the updated filter coefficient set.
2. The method of claim 1 , where step of updating the set of frequency dependent filter coefficients includes:
reducing the coefficient values towards zero if the phase angle differs significantly from the reference phase angle, and
increasing the coefficient values are increased towards unity if the phase angle substantially matches the reference phase angle.
3. The method of claim 1 , further including directing the filtered microphone signal to a secondary device that is one of a mobile device, a phone, an earpiece, a tablet, a laptop, a camera, a wearable accessory, eyewear, or headwear.
4. The method of claim 3 , further comprising
communicating directional data with the microphone signal to the secondary device, where the directional data includes at least a direction of a sound source; and
adjusting at least one parameter of the device in view of the directional data, wherein the parameters is directed, but not limited to, focusing or panning a camera of the secondary device to the sound source.
5. The method of claim 4 , further comprising performing an image stabilization and maintaining focused centering of the camera responsive to movement of the secondary device.
6. The method of claim 4 , further comprising selecting and switching between one or more cameras of the secondary device responsive to detecting from the directional data whether a sound source is in view of the one or more cameras.
7. The method of claim 4 , further comprising tracking a direction of a voice identified in the sound source, and from the tracking, adjusting a display parameter of the secondary device to visually follow the sound source.
8. The method of claim 1 , further including unwrapping the phase angle of the complex coherence to produce an unwrapped phase angle, and replacing the measured frequency dependent phase angle with the unwrapped phase angle.
9. The method of claim 1 , wherein the coherence function is a function of the power spectral densities, Pxx(f) and Pyy(f), of x and y, and the cross power spectral density, Pxy(f), of x and y, as:
C
xy
(
f
)
=
P
xy
(
f
)
2
P
xx
(
f
)
P
yy
(
f
)
.
10. The method of claim 1 , wherein a length of the power spectral densities and cross power spectral density of the coherence function are within 2 to 5 milliseconds.
11. The method of claim 1 , wherein a time-smoothing parameter for updating the power spectral densities and cross power spectral density is within 0.2 to 0.5 seconds.
12. The method of claim 1 where the reference phase angles are obtained by empirical measurement of a two microphone system in response to a close target sound source at a determined relative angle of incidence to the microphones.
13. The method of claim 1 where the reference phase angles are selected based on a desired angle of incidence, where the angle can be selected using a polar plot representation on a GUI.
14. The method of claim 1 where the devices to which the output signal of step is directed to at least one of the following: loudspeaker, telecommunications device, audio recording system and automatic speech recognition system.
15. The method of claim 1 , further including directing the filtered microphone signal to another device that is one of a mobile device, a phone, an earpiece, a tablet, a laptop, a camera, eyewear, or headwear.
16. An acoustic device to increase a directional sensitivity of a microphone signal comprising:
a first microphone; and
a processor for receiving a first microphone signal from the first microphone and receiving a second microphone signal from a second microphone, the processor performing the steps of:
calculating a complex coherence between the first and second microphone signal;
determining a measured frequency dependent phase angle of the complex coherence to determine a coherence phase angle;
comparing the measured frequency dependent phase angle with a reference phase angle threshold and determining if the measured frequency dependent phase angle exceeds a predetermined threshold from the reference phase angle;
updating a set of frequency dependent filter coefficients based on the comparing to produce an updated filter coefficient set; and
filtering the first microphone signal or the second microphone signal with the updated filter coefficient set.
17. The acoustic device of claim 16 , wherein the second microphone is communicatively coupled to the processor and resides on a secondary device that is one of a mobile device, a phone, an earpiece, a tablet, a laptop, a camera, a wearable accessory, eyewear, or headwear.
18. The acoustic device of claim 16 , wherein the processor
communicates directional data with the microphone signal to the secondary device, where the directional data includes at least a direction of a sound source; and
adjusts at least one parameter of the device in view of the directional data;
wherein the processor focuses or pans a camera of the secondary device to the sound source.
19. The acoustic device of claim 16 , wherein the processor performs an image stabilization and maintains a focused centering of the camera responsive to movement of the secondary device, and, if more than one camera is present and communicatively coupled thereto, selectively switches between one or more cameras of the secondary device responsive to detecting from the directional data whether a sound source is in view of the one or more cameras.
20. The acoustic device of claim 16 , wherein the processor tracks a direction of a voice identified in the sound source, and from the tracking, adjusting a display parameter of the secondary device to visually follow the sound source.